This invention relates to hard disc drives, and particularly to a method and apparatus for identifying the presence of conditions in a disc drive that are symptomatic of an impending head crash.
Direct access storage devices, such as disc drives store data for computers and other data processing and communication systems. Hard disc drives employ one or more rigid discs having storage surfaces on which data may be stored along concentric tracks. A transducing head is positioned by an actuator arm adjacent each disc surface to write data to, and read data from, tracks on the confronting surface. The head is mounted on an air-bearing slider that is arranged to aerodynamically xe2x80x9cflyxe2x80x9d a specified distance above the disc when the disc rotates at a design rotational velocity. Should the head and slider fail to maintain the specified fly height, there is a risk of a catastrophic head-disc interaction, known as a head crash.
Early in the life cycle of a disc drive, the slider and head fly at the design fly height. Occasional contact with protrusions on the disc surface may create debris that accumulates on the disc and/or the slider. Moreover, deliberate contact with the disc during take-off and landing may, over time, wear through protective overcoats and lubricants on the disc, generating more debris. Accumulated debris on the disc and slider alters the flying characteristics of the slider, causing lower fly height characteristics and greater incidences of contact, called xe2x80x9cinteraction,xe2x80x9d with the disc. Eventually, the slider interaction with the disc causes wearing of the disc, ultimately rendering it improbable that the slider will fly over some tracks on the disc. A catastrophic head crash may result, causing a loss of data and, in some cases, system failure.
Because a catastrophic head crash may cause loss of data, or even system failure, it is desirable to predict a head crash before occurrence so corrective action might be taken. Various techniques have been employed to predict possible head crashes in disc drives. Some of these techniques have employed acoustic transducers mounted to, or in, a disc drive for the purpose of detecting head-disc interference. For example, Fechner, in U.S. Pat. No. 4,812,927, describes an acoustic transducer coupled by a waveguide to the head-carrying carriage of a linear motor to detect head-disc interference. Banks et al., in the background to U.S. Pat. No. 5,539,592, describe mounting an acoustic transducer to the slider to detect head-disc interference. Similarly, Doan et al., in U.S. Pat. No. 5,168,412, describe detection and classification of protrusions on a disc by measuring interference energy levels using a special transducer mounted to a test head.
One problem with adding hardware, such as acoustic transducers, to the disc drive is that the cost of the disc drive is increased and valuable space that may be needed for other purposes is diminished. Consequently, several proposals have been made to predict head crash conditions using hardware already present on the drive. For example, the aforementioned Banks et al. patent describes detection of changes in the torque of the actuator arm motor as an indicator of possible head crash conditions. Hoyt et al., in U.S. Pat. No. 4,841,389, describe prediction of crash conditions by measuring a read amplitude of signals recovered by the head at different frequencies to identify the fly height of the head/slider. Tan et al., in U.S. Pat. No. 6,008,640, describe measuring head-disc interference using frequency modulation of the read signal from the head. However, a shortfall of these techniques is that they are not altogether reliable and are not capable of identifying which head or head/arm combination is likely to crash. There exists a need for a technique to reliably identify an impending head crash in a disc drive without additional hardware. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
In one embodiment of the invention, a head crash in a hard disc drive is predicted by periodically measuring a head-disc contact energy level on an actuator arm supporting the head. A predetermined change in energy level is identified between at least two energy level measurements.
In preferred forms of this embodiment, the head-disc contact energy is measured by measuring a vibration magnitude of actuator arm during a selected contact start-stop cycle, such as an initial contact start-stop cycle. A threshold representation is stored based on the measured vibration magnitude. Thereafter, the vibration level is periodically measured and compared to the threshold. Preferably, vibration is sensed by a microactuator that is separately operable to fine position the head relative to the disc surface to transfer data between the disc and the head.
In another embodiment of the present invention, a disc drive has an actuator arm supporting a transducing head in confronting relation to a surface of a rotatable recording disc to transfer data between the head and the disc. Sensing means is attached to the actuator arm for indicating a condition of the disc drive symptomatic of an impending crash of the head to the disc surface.
In preferred forms of this embodiment, the sensor means includes a microactuator mounted to the actuator arm and responsive to a drive signal to selectively position the head relative to the disc surface. The microactuator is responsive to vibration of the actuator arm due to contact between the head and the disc surface to provide a signal representative of a magnitude of contact energy between the head and the disc surface. A circuit is coupled to the microactuator and is periodically operable to identify a magnitude of contact energy. An indicator is coupled to the circuit and responsive to the representations to indicate presence of symptoms of an impending crash. A storage device, which may be the disc, stores a representation of a threshold energy magnitude and a level detector detects a predetermined difference between a representation of contact energy magnitude from the microactuator and the stored representation of threshold energy magnitude.
Other features and benefits that characterize embodiments of the present invention will be apparent upon reading the following detailed description and review of the associated drawings.